WASHINGTON — Carl Portman remembers watching, heartbroken, from Anchorage in 2005 as a Senate effort to allow drilling in the Arctic National Wildlife Refuge lost by two votes. Now, 12 years later, another effort to open up the reserve to oil and gas drilling is working its way through Congress. And this time, the political winds have shifted.

Portman, now a top official of a pro-drilling group, has seen oil revenue improve the schools, roads and hospitals in Alaska, his home state. He said he was cautiously optimistic about the drilling measure, which is included in a sweeping bill to overhaul the tax code. Environmental activists and their allies in Congress, on the other hand, are on the cusp of forever losing the decades-long political battle over the refuge.

"It is critically important and I don't think anybody knows it is stuck in a tax bill," said Sen. Maria Cantwell, the Washington Democrat who led the 2005 fight against drilling in the refuge. "It's been around for thousands of years, and for no good reason we're going to change it? Is there no such thing as a special place?''

The current effort to allow drilling, the latest in a long series, stands the best chance of success in years because of a rare alignment of the political stars: Republicans control the House, the Senate and the White House. The tax bill is critical to the political future of the president and the Republican Party. And, the linchpin: A key role belongs to Sen. Lisa Murkowski, R-Alaska, who has worked to allow drilling in the refuge her entire career.

The political landscape in Washington has also become more polarized since the last time Arctic drilling was a real possibility. When Cantwell tried to strip the drilling provision out of the budget bill in October, it failed mostly along party line votes. Sen. Susan Collins of Maine was the only Republican to support the effort.

The moment seems certain to be decisive on both sides of the battle.

Drilling proponents see the measure as one of responsible energy development for the good of Alaska and the nation. Oil and gas production in a portion of the refuge would generate $1.1 billion over the next decade, according to the nonpartisan Congressional Budget Office. And, proponents note, every barrel of oil from America is one not purchased from overseas.

For environmental activists, protecting the refuge is about preserving the fragile beauty of the Arctic wilderness — where caribou herds calve, polar bears den and millions of migratory birds gather — just as the effects of global warming are becoming more pronounced in the far north than almost anywhere else on earth.

At the heart of the debate, the opposing sides agree, is a clash of values. What is more important: the environment or economic development?

"Is this too sacred a ground to be disturbed by oil and gas drilling? It's a question of what we are willing to accept as a society," said Mark Myers, former director of the U.S. Geological Survey and a former Alaska Department of Natural Resources commissioner.

Myers said he believed that drilling could be achieved with strong environmental protections. But, he acknowledged, the choice of whether to open the Arctic is a visceral one.

"Is it painting a mustache on the Mona Lisa?" he said. "That's the fundamental question Congress has to wrestle with."

The origins of the battle over the refuge date back decades.

President Dwight D. Eisenhower placed the area under federal protection in 1960. Twenty years later, President Jimmy Carter expanded the refuge and set aside 1.5 million acres between the Brooks Range and the Beaufort Sea — known as the 1002 area, after the provision that created it — to be set aside for the possible study of oil and gas development.

The law left it to Congress to decide whether to allow drilling in the 1002 area, drawing the fault lines that would define the political battle. Since then, successive Republican efforts to open the refuge have failed in Congress or been killed by presidential vetoes.

The closest drilling advocates came to success was in 2005, but Cantwell, who was a freshman senator at the time, mounted a filibuster that ultimately stopped a provision in a military spending authorization that would have opened the refuge.

This time, the decisive role could fall to Murkowski, the chairwoman of the Senate's energy panel who has introduced legislation to open the Arctic wilderness every term she has served in the chamber.

"Right now, Lisa Murkowski may well represent the 50th vote, and that puts her in the driver seat to ask for whatever she wants. The things she seems to want most is opening the Arctic refuge," said Niel Lawrence, Alaska program director for the Natural Resources Defense Council.

Even the most ardent opponents of opening the Arctic refuge, often referred to by its acronym ANWR, say they realize this could be the week they definitively lose the legislative battle over drilling. But neither side is ready yet to acknowledge defeat or to declare victory.

Portman, deputy director of Alaska's Resource Development Council, said he would not celebrate until a bill was signed into law. "I just don't want to get my hopes up so much and set myself up for another disappointment," he said. "I will not be standing up applauding until I see a vote that is in our favor and it goes to Congress and ends up on the president's desk."

To be sure, the tax bill could still collapse. Even if it passes, the Senate bill will have to be reconciled with a version that passed the House of Representatives that does not currently include the drilling provision. Moderate Republicans, some say, could still sink the effort.

"We've seen it before," said Byron L. Dorgan, a Democratic former senator from North Dakota who is now lobbying to block drilling. "The potential exists to have some people say, 'If ANWR is in, I'm out of it.' We'll see. Anything is possible."

Drilling supporters say they are grateful that Congress appears poised to send a message that economic prosperity is the government's primary goal.

"It's a very strong message to the people of America that we are on a very different pathway now," said Gail Phillips, a former speaker of the Alaska House of Representatives. Phillips, who has called the refuge a "frozen wasteland," said allowing drilling there would send an important signal that "there are other big projects and we are open to doing these things."

For all the brave words of environmental activists, that's precisely the prospect that worries them most. If they lose the fight over the Arctic refuge, they say, there's no telling what could be lost next.

"This is one of the unique places on the planet," Dorgan said. "Is everything for sale?"